The present invention generally relates to a hand tool for use in the maintenance of an internal combustion engine. More specifically, the present invention relates to a tool for removing and reinstalling a valve from within a valve guide in an aircraft internal combustion engine.
Aircraft engines, like many other types of internal combustion engines, include a valve positioned in each cylinder of the internal combustion engine that opens and closes to provide access to an exhaust port. The exhaust port allows the volume of exhaust gases contained within the cylinder to be discharged after combustion has occurred within the cylinder. Each valve generally includes a valve head connected to an elongated valve stem. The valve stem is guided through its reciprocating movement by a valve guide having an inner diameter slightly larger than the external diameter of the valve stem.
After extended periods of use of an internal combustion engine, airborne carbon particles entrained within the exhaust discharged from the cylinder through the exhaust port begin to build up on the inner diameter of the valve guide. The carbon build up on the inner diameter of the valve guide reduces the tolerance between the valve guide and the valve stem. Eventually, the carbon build up on the inner diameter of the valve guide can cause the exhaust valve to freeze up and no longer function properly. The freeze up of the valve stem within the valve guide can cause the internal combustion engine to malfunction and possibly shut down.
Since complete shut down of an internal combustion engine in an aircraft can have disastrous consequences, the engine manufacturers suggest that the individual valve guide for each cylinder in the internal combustion engine should be cleaned after a predetermined number of hours of operation of the internal combustion engine. For example, some aircraft manufacturers suggest that the valve guides be cleaned after 400 hours of operation of the aircraft engine.
During the maintenance and cleaning of the valve guides, the valve itself must be removed from the valve guide and the inner diameter of the valve guide is cleaned and re-bored by a conventional boring tool. Although the actual maintenance performed on the valve guide is rather simple and quick, a substantial obstacle in cleaning the valve guides is the removal and insertion of the valve from the valve guide prior to and after the cleaning.
Currently, two common methods are used for cleaning the valve guides of an internal combustion engine. The first method requires completely disassembling the engine and removing each valve by pushing the valve into the hollow cylinder of the engine. Once the valve has been removed from the valve guide, a cleaning device can be used to re-bore the valve guide. This type of maintenance on an internal combustion engine can require up to 24 hours of labor, and thus be extremely expensive for the aircraft owner.
Alternatively, a method of cleaning the valve guides has been suggested in which the retainer attached to the end of the valve stem is removed and the entire valve is pushed into the cylinder. Once the valve has been pushed into the cylinder, the valve guide can be bored and cleaned as discussed. After the valve guide has been cleaned, individual finger-like grippers can be used to reach into the cylinder through the exhaust port and grasp the valve within the cylinder. Once grasped, the end of the valve stem must be guided into the opening of the valve guide. However, this method of removing and replacing the valve has proven to be extremely difficult and very time-consuming due to the tedious process of attempting to grasp the valve once it has fallen into the cylinder of the internal combustion engine. In practice, this method of removing and replacing the valve has proven impractical, since it can often require ten or more hours to clean each valve guide of the internal combustion engine.
Therefore, a need exists for an improved method of removing the valve from within the exhaust port of an internal combustion engine without either disassembling the entire engine or requiring the engine mechanic to fish the valve out from within the open cylinder. Further, it is an object of the present invention to provide a tool that can be used to securely grasp the valve prior to the valve being removed completely from the valve guide. Additionally, it is an object of the invention to provide a tool that securely grasps the valve such that the valve can be removed and repositioned within the valve guide without losing positive control of the valve.
The present invention is a grasping tool for securely holding a valve such that the valve can be removed and reinstalled from within a valve guide. The grasping tool maintains a secure hold on the valve such that the valve can be removed and the valve guide cleaned by appropriate methods. Once the valve guide has been cleaned, the grasping tool can be used to guide the valve back within the valve guide.
The grasping tool of the present invention includes a hollow, elongated shaft extending between a first end and a second end. The hollow, elongated shaft includes an open passageway extending between the first and second ends. The elongated shaft includes an angled section to permit the tool to be inserted into the cylinder through the exhaust port.
A grasping head is attached to the first end of the elongated shaft. The grasping head includes a pair of legs separated by an arcuate contact surface. The arcuate contact surface is configured to receive and engage the outer circumference of the valve being removed.
A handle is movably mounted on the elongated shaft near the second end of the elongated shaft. Specifically, the elongated shaft includes a threaded portion having external threads that are received within an internally threaded mating section formed on the handle. Rotation of the handle about the elongated shaft causes the handle to move along the length of the shaft.
A fixed length cable extends through the combined length of the handle and elongated shaft and an adjustable length portion of the cable forms a securing loop extending from the grasping head. A first end of the cable extends through one of the legs of the grasping head and includes a stop member that prevents the first end of the cable from passing back through the leg of the grasping head. The second end of the cable passes through the opposite leg of the grasping head and is movable relative to the grasping head such that the length of the securing loop extending from the grasping head is adjustable. In the preferred embodiment of the invention, the second end of the cable extends through the combined length of the elongated shaft and handle and extends out past the outer end of the handle. A locking member is attachable to the cable near the outer end of the handle to create a fixed length for the cable between the locking member and the stop member on the first end of the cable.
The grasping tool of the invention can be used to securely grasp the valve stem of a valve that is to be removed from the valve guide to be cleaned. Initially, the length of the securing loop is increased by rotating the handle relative to the elongated shaft. Once the length of the securing loop has been sufficiently increased, the securing loop is passed over the head of the valve such that the valve stem is positioned between the securing loop and the grasping head. The retainer attached to the end of the valve stem can then be removed and the piston contained within the cylinder is moved into contact with the valve head. Once the valve head is supported by the piston, the valve is then pushed from the valve guide until only the end portion of the valve remains within the valve guide. The length of the securing loop is then reduced by rotating the handle relative to the elongated shaft until the valve stem is securely entrapped between the securing loop and the grasping head. Once the securing loop has been sufficiently tightened, the valve can be fully removed from the valve guide.
After the valve guide has been cleaned, the grasping tool can be used to lift the valve back into the valve guide. Once the valve has been reinserted back into the valve guide, the piston is moved back into contact with the valve head to support the valve. Once supported by the piston, the handle of the grasping tool is rotated such that the securing loop is lengthened and the grasping tool is removed from the valve. Once the grasping tool has been removed, the valve can be fully inserted back into the valve guide and the engine returned back to normal operating conditions.
Because of the ability for the grasping tool to tighten very securely around the valve, the grasping tool can be used to remove and reinsert the valve into the valve guide, even though the tolerances between the valve guide and the valve are very small. Additionally, since the valve is always in the control of the engine mechanic, there is little chance that the valve will fall into the cylinder chamber and become lost, thereby requiring complete disassembly of the engine.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.